1. Field of the Invention
This invention relates to a process for welding a fixture pipe to each end of a stabilizer which serves to alleviate rolling of a vehicle.
2. Description of the Prior Art
To weld fixture pipes to opposite ends of a hollow stabilizer""s suspension arm, each end surface of the hollow stabilizer""s suspension arm a has conventionally been machined to form a concave b in conformity with an outer peripheral surface of each fixture pipe c, as shown in FIG. 4 of the accompanying drawings. Then, these two parts are rotated with said concave b held against the outer peripheral surface of the fixture pipe c to arc weld these two parts together. In this manner, bead d is formed between the respective outer peripheral surfaces of the hollow stabilizer""s suspension arm a and the fixture pipe c as shown in FIG. 5.
However, such conventional welding process has disadvantages lying in that the welding process is inevitably complicated; it is difficult to hold two parts in close surface contact; bead is formed not around the inner peripheral surface but only around the outer peripheral surface of the hollow stabilizer""s suspension arm and therefore improvement of a joining effect is limited; during the arc welding, complicated arrangements are necessary to rotate two parts to be welded together as they are held in desired relative position because the hollow stabilizer""s suspension arm and the fixture pipe are neither welded nor bonded together prior to the arc welding.
This invention aims to solve the problems as have been described above.
The object set forth above is achieved, according to the invention, by resistance welding the fixture pipe to each end of the hollow stabilizer""s suspension arm and then subjecting the resistance welded zone to arc welding. In this way, none of machining steps is required prior to welding and, in consequence, the welding process is correspondingly simplified. Additionally, the resistance welding ensures the end of the hollow stabilizer""s suspension arm to be reliably welded to the fixture pipe not only along the outer peripheral surface but also along the inner peripheral surface of said end. Such double process of resistance welding and arc welding drastically improves a welding effect, on one hand, and simplifies the steps of the process, on the other hand, because the step of arc welding can be performed with the hollow stabilizer""s suspension arm and the fixture pipe already joined together by the previous step of resistance welding.
The ends of said hollow stabilizer""s suspension arm are subjected to upsetting to form thick-wall portions, respectively, before said steps of resistance welding and arc welding. This advantageously enlarges a sectional area around which the hollow stabilizer""s suspension arm should be welded to the fixture pipe and thereby improves a welding effect.
Also, in accordance with the invention, the hollow stabilizer""s suspension arm is made of seam welded steel pipe containing, in % by weight C: 0.05xcx9c0.07, Si: 0.55xcx9c0.65, Mn: 1.90xcx9c2.10, P: less than 0.030, S: less than 0.010, Ti: 0.08xcx9c0.12, Nb: 0.03xcx9c0.05 and Ca: 0.002xcx9c0.006. A content of carbon is adequately low to prevent a weld zone from being hardened and becoming brittle due to a welding heat; and
The hollow stabilizer""s suspension arm has a wall thickness of 1.5xcx9c2.5 mm at its tip prior to resistance welding. Such dimensioning ensures an appropriate penetration for reliable welding.
In addition, the arc welding starts from a point on the seam welded steel pipe remote from its seam. By selecting a starting point of the arc welding in this manner, the arc welding can be stabilized on the seam and therefore there is no apprehension that a strength of the seam welded steel pipe might be deteriorated at the seam.
FIG. 1 is a side view showing a fixture pipe ready to be welded to an end of a hollow stabilizer""s suspension arm using a process according to one preferred embodiment of the invention as partially broken away;
FIG. 2 is an enlarged sectional view of a weld zone;
FIG. 3 is a front view of the fixture pipe after being welded to said hollow stabilizer""s suspension arm;
FIG. 4 is a view similar to FIG. 1 but relating to the case of prior art:
FIG. 5 is a view similar to FIG. 2 but relating to the case of prior art;
FIG. 6 is an axial sectional view showing an end of the stabilizer""s suspension arm;
FIG. 7 is a graphic diagram indicating a result of endurance test conducted for the stabilizer.